This application claims priority under 35 U.S.C. §119 from European Patent Application No. 050 07 339 filed Apr. 5, 2005, incorporated herein by reference in its entirety.
The invention relates to an arrangement of magnets.
In a sputter system, plasma is generated in a sputter chamber under vacuum. The plasma is understood to be a quasi-neutral many-particle system in the form of gaseous blends of free electrons and ions as well as possible neutral particles, i.e. atoms, molecules or radicals. Positive ions of the plasma are attracted by the negative potential of a cathode, which features a so-called target. The positive ions impinge upon this target and knock away small particles that subsequently precipitate on a substrate. The knocking away of these particles is referred to as “sputtering.” The plasma contains ionized gases, which can, for example, be inert gases such as argon, in the event of a non-reactive sputtering. In the event of a reactive sputtering, for example, oxygen is either used by itself or in conjunction with an inert gas.
The ions required for the sputtering process are generated through the collisions of gas atoms and electrons in a glow discharge and accelerated into the target forming the cathode with the assistance of an electric field.
In conventional DC and HF sputtering, only few secondary electrons, emitted on sputtering the target, contribute to the ionization of the sputter gas atoms.
To improve the sputter effect, magnets are utilized near the target. Their magnetic field keeps the plasma at the target. Through the interaction of the magnetic and the electric fields the charge carriers in the plasma primarily no longer move parallel to the electric field but also at right angles to it, which results in cycloid electron trajectories. As the deflection radii of the electrons are much smaller than those of the ions, due to their low mass, the electrons concentrate before the target surface. Therefore, the probability that sputter gas atoms are ionized via collisions with electrons is much higher. As a result of the E×B drift of the electrons—the electrons follow a trajectory referred to as racetrack—and the concentration of plasma before the target surface, the electrons no longer fly directly to the substrate. Heating of the substrate is therefore reduced.
The much heavier ions fall onto the target, which has the effect of a negative electrode or cathode and sputter this. Ionizations therefore largely occur where the magnetic field vector is parallel to the target surface. The plasma is most dense here, as a result of which the target is most strongly eroded at this point. The glow discharge plasma is virtually enclosed by the magnetic field and the electron trajectories are extended by the fact that the electrons rotate around the magnetic field lines serving as axes, thereby increasing the rate at which gas atoms and electrons collide.
To coat larger areas, planar magnetrons are generally used. These, however, have a lower target utilization, e.g. of 40% or less.
As a result, rotating cylinder magnetrons, which achieve a target utilization of 90% and more, have been used more frequently in recent times.
A disadvantage which both cylinder magnetrons, which are occasionally also referred to as pipe cathodes, and planar magnetrons feature is the irregular wear of the targets. Pipe cathodes are less sputtered on the edges where in fact a re-coating can occur. So-called racetracks form in the planar magnetrons, i.e. trenches from erosion caused by the arrangement of the magnets in the magnetrons. These erosion trenches are directly generated by the colliding ionized gas particles. These hit the target, acting as a negative electrode or cathode and serving as a sputter, in an irregular way. The plasma trajectory determined by the magnetic field—which correlates with the electron trajectories—or the racetrack, in particular delimits the target utilization of planar magnetrons; when the target is fully eroded at a given point, it can no longer be used, even if there is still sufficient material at other points. Although even a cylinder magnetron has a plasma racetrack when stationary, which corresponds with the configuration of the magnets, no trench-like depression is formed on the rotating target.
Apart from the tube-like racetrack erosion, the rectangular planar magnetrons with straight racetracks additionally feature a so-called cross corner effect, which also delimits utilization of the target. Cross corners are the diagonally opposite corners of a rectangular magnetron. If the magnetic field in a terminal region of the magnetron cathode differs from the magnetic field in the central area, e.g. is weaker, the electrons drift faster in this terminal region than in the middle, i.e. they quickly arrive in the cross corner area. This causes electron congestion in this area, which results in a denser ionization and subsequently in increased erosion of the target. (cf. Q. H. Fan, L. Q. Zhou and J. J. Gracio, A cross-corner effect in a rectangular sputtering magnetron. J. Phys. D: Appl. Phy. 36 (2003), 244-251).
A magnetron sputter system already exists in which double T-shaped magnets of an initial polarity are surrounded by rectangular framework magnets of a second polarity (U.S. Pat. No. 5,458,759). This makes use of the arrangement of the magnets to achieve a consistent as possible wear of the target.
Another procedure is also based on the assumption that the arrangement of magnets causes the erosions on the target (DE 197 01 575 A1). In so doing, it suggests the positioning of a substrate in a direction perpendicular to the lengthwise direction of the cathode, while the magnets of the cathode are arranged so that they form two closed loops of a sputtering erosion surface area and can be moved perpendicular to the lengthwise direction of the cathode.
Furthermore, a sputter system exists with magnets that are arranged in a meander-like fashion (EP 0 105 407, FIG. 5). This generates a pre-determined plasma sputtering area in the form of a meandering electron trajectory, which guarantees a relatively constant wear of the target. With this sputter system, no relative movement of target and magnet system occurs. As a result, a re-coating between the individual meander loops can occur and the target—which is larger than the substrate—cannot be fully sputtered.
Another existing magnetron sputtering cathode features an internal magnetic south pole with a central bar from which tongues extend outwards at right angles in regular intervals (EP 0 242 826 B1=U.S. Pat. No. 4,826,584). Here the exterior magnetic north exists of a rectangular framework, from the lengthwise sides of which tongues extend inwards at right angles that are arranged so that they lie between two tongues each of the magnetic south. This results in a meander-shaped magnetic field and thus a meander-shaped erosion zone. The tongues of the south pole are all parallel to each other. Once again, with this sputtering cathode there is no relative movement between the target and the magnetic system.
A magnet arrangement for a sputter system also exists in which a magnetic north framework surrounds a linear south pole (Patent Abstracts of Japan, Vol. 013, no. 169 (C-587) & JP 63317671 A, FIG. 8). Between this north and south pole there are further north and south poles to the right and the left of the linear south pole, which, however are not connected to this south pole.
Furthermore, a magnet arrangement for a sputter system exists in which a largely ring-shaped north pole surrounds a linear south pole and in which the end of the south pole has arms extending to the north pole (U.S. Pat. No. 5,182,003). These arms are, however, not offset against each other.
Finally, a magnet arrangement for a sputter system exists in which an initial oval magnetic pole surrounds a second linear magnetic pole (U.S. Pat. No. 5,026,471). Neither of the two magnetic poles has arms extending from it.
The invention is based on the task of optimally utilizing large targets by means of a suitable management of erosion trenches and to keep the target as free as possible of re-deposits.
This problem is solved according to the present invention.
The invention thus pertains to a magnet arrangement for a planar magnetron in which an initial magnetic pole encompasses a second magnetic pole. This magnet arrangement is moved linear in lengthwise direction to a target by a specific value, and then moved back in the opposite direction by the same value. In one version an additional perpendicular movement is also effected. The magnet arrangement is designed so that the north and south poles interlock to form waviform racetracks. As a result, constant sputtering from the entire target surface can be effected.
The benefit achieved by the invention consists of the fact that large and plane targets with only a single erosion trench can be coated so that more than 50% of its surface is covered by the erosion trenches. Through the relative movement between the target and magnet system this results in a homogeneous erosion profile. Through the slight interlocking of opposing magnetic pole elements sputtering is also effected in the middle of the target.
If the invention is advantageously designed, even long, wide targets with only a single racetrack or erosion track can be coated. As the two poles of the magnet arrangement interlock slightly in the middle, it is possible to achieve a high target utilization and a virtually complete re-coating free target surface with only one linear movement. In so doing, north and south pole are arranged relatively to each other so that meander-like racetracks are achieved on the target. Two opposing meanders are so close to one another that the target surface is evenly sputtered when executing a linear movement toward the target length. The height of lift is ± half a meander interval.
Embodiment examples of the invention are shown in the drawings and are subsequently described in more detail.